DE60035949T2 - Method for controlling the speed of an induction motor - Google Patents

Description

BACKGROUND OF THE INVENTION

The The present invention relates to a speed control method for a Induction motor and in particular a technique of vector control without a speed sensor that does not have a speed sensor attached to a motor requires and makes it possible to get a high torque at a zero speed range starts.

As a method of controlling the rotational speed of an induction motor, a method of vector control without a rotational speed sensor is conventionally known. 14 shows the configuration of his control system. The reference number 1 denotes an induction motor; 2 a power inverter for outputting an output voltage proportional to a voltage command value V1 *; 3 a coordinate transformer for effecting a coordinate transformation of inverter output currents iu and iw and calculating d-axis and q-axis currents id and iq; 4 a voltage calculation unit for calculating a value of a creeping impedance voltage drop of the motor based on id, iq and an output frequency command value ω1 *; 5 and 6 Adders for adding the voltage drop value to the induced electromotive force command values ed * and eq * and outputting the d-axis and q-axis voltage command values Vd * and Vq *; 7 a reference phase generator for integrating ω1 * and outputting a reference phase θ; 8th a coordinate transformer for outputting an inverter output voltage command value V1 * (three-phase) based on Vd * and Vq *; 9 a calculation unit for outputting a slip frequency calculation value ωs1 based on id and iq; 12 an adder for adding ωs1 to a speed command value ωr * and outputting ω1 *; and 13 an electromotive force calculating unit for calculating eq * based on ω1 *.

It Note that Okuyama et al .: "Simplified Vector Control System without Speed and Voltage Sensors - Effects of Setting Errors in Control Parameters and their Compensation, The Transactions of The Institute of Electrical Engineers of Japan, Vol. 110-D, No. 5, May 1990, p. 477-486, is known as a related document.

JP-11018497 discloses a speed control method for an induction motor. The to be solved Problem is the increase the torque at the time of low speed. To this end the q-axis current command value is brought to zero when the Amount of a speed command value or a speed estimate is less than a set value. Furthermore, a value is used which is determined from a frequency determined on the basis of Difference between the speed command value and the speed estimated value is estimated. The d-axis current command id * and the q-axis current command iq * both become for the Control used.

JP-11187699 discloses a speed control method for an induction motor. The to be solved Problem is the prevention of a torque shortage in a zero speed range by controlling a magnetic flux-axis current so that it is at least the ordinary one Time value is when a speed command value is almost at a specified value is, replacing a frequency command value with a speed estimate and performs an operation based on the speed command value. Of the d-axis current command id * and the q-axis current command iq * both used for control.

SUMMARY OF THE INVENTION

In the above-described configuration, the operating frequency becomes ω1 of the motor 1 controlled in proportion to ω1 * and the drop of the creeping impedance is determined by the action of the voltage calculation unit 4 compensated. As a result, regardless of the magnitude of the torque, the induced electromotive force e of the motor changes 1 Not. Therefore, the magnetic flux of the motor is always kept constant, and a decrease in the torque due to a loss of the magnetic flux of the motor is prevented. At this time, since iq is proportional to the slip frequency ωs, when the calculation unit becomes 9 estimates ωs according to the following formula (1) and adds them to ωr * for calculating ω1, compensating for the variation of the real speed speed ωr due to a change in the slip (torque). ωs = 1 / T2 · iq / id (1)

However, in cases where the actual values r1 and Lσ of the engine parameters vary from the reference values r1 * and Lσ * in the voltage calculation unit 4 used motor parameters vary, the magnetic flux of the motor according to the torque. As a result, a decrease in torque occurs (the torque can no longer be proportional to the current). In addition, since iq and ωs are not proportional, the formula (1) is not valid, so that the accuracy of the above-mentioned compensation for the speed fluctuation deteriorates.

In general, a decrease in torque and the deterioration of the speed accuracy in the zero-speed range and its Um noticeable.

Accordingly It is an object of the present invention, a speed control method for a To provide induction motor, which is a control structure for Avoiding a decline of the torque in the low speed range allowed.

These The object is achieved by a method according to claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

1 Fig. 10 is a block diagram of a vector control apparatus without a speed sensor for realizing a speed control method for an induction motor according to a first embodiment of the invention;

2 is a diagram used to explain the operation of the in 1 useful device shown;

3 is a diagram used to explain the operation of the in 1 useful device shown;

4 is a vector diagram of the engine used to explain the operation of the in 1 useful device shown;

5 Fig. 10 is a block diagram of the vector control apparatus without a speed sensor for realizing the speed control method for an induction motor according to another embodiment of the invention;

6 is a diagram used to explain the operation of the in 5 useful device shown;

7 FIG. 15 is a diagram for explaining the contents of an arithmetic operation by a d-axis current command unit in the in. FIG 5 useful device shown;

8th Fig. 10 is a block diagram of the vector control apparatus without a speed sensor for realizing the speed control method for an induction motor according to still another embodiment of the invention;

9 is a diagram used to explain the operation of the in 8th useful device shown;

10 FIG. 15 is a diagram for explaining the contents of an arithmetic operation by a d-axis current command unit in the in. FIG 8th useful device shown;

11 Fig. 10 is a block diagram of the vector control apparatus without a speed sensor for realizing the speed control method for an induction motor according to another embodiment of the invention;

12 is a diagram used to explain the operation of the in 11 useful device shown;

13 FIG. 15 is a diagram for explaining the contents of an arithmetic operation by a d-axis current command unit in the in. FIG 11 useful device shown; and

14 FIG. 10 is a block diagram illustrating the configuration of a conventional speed control apparatus for an induction motor.

DESCRIPTION OF THE EMBODIMENTS

It A description will now be made with reference to the drawings the embodiments the invention.

1 FIG. 12 is a block diagram of a vector control apparatus without a speed sensor for realizing the speed control method for an induction motor according to an embodiment of the invention. FIG. The reference numerals 1 to 9 . 12 and 13 denote constituent elements identical to those of the conventional example.

The reference number 10 denotes a calculation unit for determining a slip frequency calculation value ωs2 on the basis of the induced electromotive force command values ed * and eq *; 11 an adder for adding the aforementioned ωs1 and ωs2 and outputting a slip frequency estimated value ωs ^; 12 an adder for adding ωs ^ to ωr * and outputting ω1 *; 14 a d-axis current command unit for outputting a d-axis current command value id * greater than a normal value; 15 an amplifier for outputting a voltage command value ed * according to a deviation between id * and id, wherein a gain Gd is adjusted to change according to ωr *; and 16 a gain command unit for commanding the gain Gd 17 denotes a q-axis current limiter for controlling iq substantially to zero in a zero-speed range, wherein a gain Gd is adjusted to change according to ωr *. The reference number 18 denotes a gain command unit for commanding the gain Gq.

Next, a description will be given of the operation of the entire system. The operation of the constituent elements 1 to 9 . 12 and 13 is the same as described above in the related art section. The object of the present invention is to prevent a decrease in the torque due to variations of the motor parameters in the prior art, and the constituent elements, denoted by the reference numerals 10 . 11 and 14 to 18 are a characteristic configuration of the present invention. The constituent elements 14 to 16 are for controlling the d-axis current id to a predetermined value which is larger than a normal value in the zero-speed range, and a deviation between the command value id * from the d-axis current command unit 14 and the detected value id from a coordinate transformer 3 is through the amplifier 15 reinforced and ed * is output. In other ranges than the zero speed range, the output ed * is from the amplifier 15 is controlled to be in accordance with the gain command Gd from the amplification command unit 16 Zero approaches. 2 Fig. 15 shows the relationship between the gain command Gd, the d-axis current id and the speed command value ωr *.

Meanwhile, in the zero-speed range eq * by the current limiter 17 corrected to essentially control iq to zero. The input / output relationship of the command unit 18 is in 3 shown. Since the gain Gq takes a large value in the zero-speed range, eq * becomes an output value Gq · iq of the q-axis current limiter 17 corrected in one direction to suppress iq. As a result, iq is essentially controlled to zero.

A vector diagram concerning the current and magnetic flux of the motor is in 4 shown. The engine-generated torque t is shown by the following formulas (2) and (3): τ = k (Φ2d · iq-Φ2q · id) = -kΦ2q · id (2) where iq = 0, 2q <0 (motor driven operation) and k is a proportional coefficient.

Or τ = kM · in · it = kM (id 2 / 2) · sin (2 · θΦ) (3) where θΦ is an angle formed by the magnetic flux Φ2 and the current id, and M is the excitation inductance.

From Formula (3), the torque at 2 x θφ = 90 ° assumes a maximum value proportional to an id ² value, and the torque changes from positive to negative in the range of -45 ° C ≦ θφ ≦ 45 °. Namely, an entire area covering the engine-driven operation and regenerative braking can be uniformly controlled. In addition, in this case, the motor-generated torque changes in accordance with θΦ and is not affected by the motor parameters r1 and Ls. For, according to the control method of the invention, even in a case where there are variations in the engine parameters, a decrease in torque occurs neither in the engine-driven operation nor in the regenerative braking.

In the above zero speed range, a real slip frequency ωs is expressed by the following formula (4): ωs = 1 / T2 * it / im = -1 / T2 * Φ2q / Φ2d (4)

As shown in formula (4), the relational expression differs from the case for the normal range (formula (1)). For this reason, in the zero-speed range, the slip frequency calculation value ωs2 is calculated by the calculation unit 10 calculated using ed * and eq * according to the following formula (5): ωs2 = 1 / T2 * ed * / eq * (5) in which ed * ≒ -ωr · Φ2q eq * ≒ω1 · Φ2d

Through the entire range including the zero speed range and the normal ranges, ωs1 and ws2 are passed through the adder 11 and the ωs ^ shown in the following formula (6) is output. ωs ^ = 1 / T2 * iq / id + 1 / T2 * ed * / eq * (6)

in the Zero speed range, the formula (6) is the same as the formula (5) since lq ≒ 0 and in the normal range, the formula (6) is the same as the formula (1), since ed * ≒ 0.

Since ωs ^ adds to ωr * In order to effect slip compensation, the real rotational speed ωr becomes constant held, even if the slip (the torque) varies, so that a speed control with high accuracy are effected can.

It should be noted that in the area where Φ2q does not change much, eq * as per can be considered proportional to ω1, so that the calculation is performed using ω1 * instead of eq * in formula (6). Besides, it is possible to use not only ω1 * but also ωr *.

5 shows a further embodiment of the present invention. The difference to the in 1 in the embodiment shown is that id * is reduced at ω1 * ≒ 0, and the relationship between ω1 * and id * is in 6 shown.

Since the line state is not shifted between elements of the inverter and a current is concentrated on certain elements, when ω1 * = 0, it is necessary to limit the inverter output current to a normal level by comparison. The content of the calculation by a current command unit 14a is in 7 shown. The calculation shown in the following formula (7) is performed by a function generator 141 , a delay circuit 142 and an adder 143 performed and it will id * with the in 6 shown relationship issued. Id * = id0 * - Δid1 id0 * - 1 / (1 + TS) * F (ω1 *) (7)

It should be noted that the delay circuit 142 for considering the transient capacitance (a delay in the temperature rise) of the elements with respect to the concentration of the current, and id0 * is a reference value in a case where there is no concentration of the current.

The configuration of constituent elements other than the current command unit 14a is the same as the one in 1 embodiment shown and also their operation is the same.

It should be noted that in the area where Φ2d not big changes, eq * as proportional to ω1 can be considered, so that in formula (8) the calculation by Use of ω1 * instead of eq * can be. Furthermore Is it possible, not only ω1 *, but also ωr * to use.

8th illustrates still another embodiment of the present invention. The difference to the in 1 and 5 shown embodiments is that id * is made variable in accordance with the torque in the zero-speed range, and 9 shows the relationship between id * and the torque. In the in 1 and 5 In the embodiments shown id * is more than necessary during a light load because id * is fixed regardless of the relative magnitude of the torque, so that the engine loss (copper loss) increases by that margin. For this reason, it is preferable to reduce the inverter output current during low torque.

The content of the arithmetic operation by a current command unit 14b in the present embodiment is in 10 shown. The reference number 19 denotes a calculation unit (divisor) which generates a ratio ed * / eq *. The calculation shown in the following formula (8) is performed by a function generator 141b and the adder 143 by using ed * / eq * from the calculation unit 19 which is a value corresponding to the slip (torque) of the engine, and it becomes id * with the in 9 shown relationship issued. id * = id0 * - Δid2 = id0 * - G (ed * / eq *) (8) where id0 * is a reference value corresponding to a maximum torque.

The configuration of constituent elements other than the current calculation unit 14b and the calculation unit 19 is the same as the one in 1 embodiment shown and also their operation is the same.

11 illustrates another embodiment of the present invention. In this embodiment, id * is varied in accordance with ω1 * and the torque in the zero-speed range. 12 shows the relationship of id *, ω1 * and the torque.

The content of the arithmetic operation by a current command unit 14c in the present embodiment is in 13 shown. The function generators 141 and 141b and the delay circuit 142 are similar to those of the embodiments described above. Their outputs Δid1 and Δid2 become a maximum value selecting circuit 144 and the larger of these values is output as Δid. Furthermore, id * is calculated in accordance with formula (9). As a result, id * changes in accordance with 12 ,

The configuration of constituent elements other than the current command unit 14c and the calculation unit 19 is the same as the one in 1 embodiment shown and also their operation is the same. Id * = id0 * - Δid (9)

It should be noted that in the same manner as in the above-described embodiments, as for ed * / eq * from the calculation unit 19 , ie the input signal of the functi onsgenerators 141b , in the range where Φ2d does not change large, eq * can be considered proportional to ω1 *, so that the calculation can be performed by using ω1 * instead of eq *. Besides, it is possible to use not only ω1 * but also ωr *.

As As described above, according to the above-described embodiments itself in cases, in which there are variations in the engine parameters, the speed control an induction motor is also stable in its recovery operation be effected.

Claims (1)

A speed control method for controlling an induction motor connected to a power inverter by controlling the output voltage and the output frequency of the inverter ( 2 ) in accordance with a speed command (ωr *) or a frequency command (ω1 *), the output voltage and the output frequency of the power inverter being controlled by a controller ( 8th ) are controlled by using a d-axis voltage command (Vd *) and a q-axis voltage command (Vq *) and a reference phase (θ) so that the induction motor has a torque τ according to the formula τ = kM (id 2 / 2) sin (2θΦ) where k is a proportionality coefficient, M is the excitation inductance, id is a d-axis current, and θφ is the angle between magnetic flux Φ2 and id, and when the magnitude of the velocity command (ωr *) or the frequency command (ω1 *) is equal to or less than a set value, the d-axis current (id) is set to a value greater than a normal value, the normal value being a value at which the magnitude of the velocity command (ωr *) or the frequency command (ω1 *) is greater than or equal to the set value, correcting a q-axis voltage command value (Vq *) in accordance with a detected value of a q-axis current (Iq) and controlling the q-axis current (Iq) into one Direction in which the q-axis current becomes zero by changing the q-axis voltage command value (Vq *), characterized in that the change of the q-axis voltage command value (Vq *) is made by setting a value, by applying a gain (Gq) subtracted from the commanded q-axis current (Iq) from a command value (eq *) of the induced q-axis electromagnetism force, the gain being chosen to be large as the magnitude of the velocity command (ωr * ) or the frequency command (ω1 *) is equal to or smaller than the set value, and 0 (zero) when the amount is larger than the set value.